1. Field of the Invention
The present invention relates to an image sensing module, and more particularly, to an image sensing module capable of determining a real image and a virtual image from received images.
2. Description of the Prior Art
FIG. 1 is a diagram showing an optical sensing system 100 of the prior art. The optical sensing system comprises a sensing area 116, a mirror 104, an image sensor 110, and a processing circuit 112. Two reflecting elements 106 and 108 are arranged at edges of the sensing area 116. The reflecting elements 106 and 108 are for reflecting light to the sensing area 116. The mirror 104 is for generating a mirror image of the sensing area 116. The mirror 104 can be a flat mirror with a mirror face 118 facing the sensing area 116. The image sensor 110 is arranged at a corner of the sensing area 116. A sensing range of the image sensor 110 comprises the sensing area 116. The processing circuit 112 is for computing a position of an object 102 according to images received by the image sensor 110 in order to generate an output coordinate Sxy.
FIG. 2 is a diagram illustrating operation principles of the optical sensing system 100. In FIG. 2, an upper part above the mirror 104 represents a mirror image generated by the mirror 104. A mirror image 106A is a mirror image of the reflecting elements 106. A mirror image 108A is a mirror image of the reflecting elements 108. A mirror image 110A is a mirror image of the image sensor 110. A mirror image 102A is a mirror image of the object 102. As shown in FIG. 2, the image sensor 110 receives a real image of the object 102 along a light path 204, and receives a mirror image 102A of the object 102 along a light path 206. FIG. 3 is a diagram showing an image captured by the image sensor 110 of FIG. 2. In FIG. 3, image 300 is an image captured by the image sensor 110. Because the image sensor 110 is arranged at a left side of the mirror, and a dark fringe 306 is closer to a left edge of the image 300 than a dark fringe 304, the processing circuit 112 can determine the dark fringe 304 corresponds to the real image of the object 102, and the dark fringe 306 corresponds to the mirror image 102A of the object 102, such that the processing circuit 112 can compute the position of the object 102 according to the dark fringes 304 and 306. The detailed computing method can be referred from U.S. Pat. No. 7,689,381. In addition, an area 302 is a bright area of the image 300 corresponding to light reflected from the mirror 104 and the reflecting elements 106 and 108. By comparing brightness of the bright area 302 and the dark fringes 304 and 306, the processing circuit 112 can obtain positions of the dark fringes 304 and 306 more accurately, in order to obtain the position of the object 102 precisely.
However, when the optical sensing system 100 is utilized to sense multiple objects, the processing circuit 112 is not able to distinguish the dark fringe corresponding to the real image of the object and the dark fringe corresponding to the mirror image of the object. FIG. 4 is a diagram showing a first situation of the optical sensing system 100 sensing two objects 102 and 103. FIG. 5 is a diagram showing a second situation of the optical sensing system 100 sensing two objects 102 and 103. FIG. 6A is a diagram showing an image 400 captured by the image sensor 110 of FIG. 4. FIG. 6B is a diagram showing an image 500 captured by the image sensor 110 of FIG. 5. As shown in FIG. 6A and FIG. 6B, the image 400 captured by the image sensor 110 of FIG. 4 is similar to the image 500 captured by the image sensor 110 of FIG. 5. The processing circuit 112 cannot determine the position of object 102 and the position of object 103, since there are two possible situations. That is, the processing circuit 112 cannot determine the dark fringes 404, 406, 504, and 506 correspond to the real images of the objects or the mirror images of the objects. In other words, the processing circuit 112 cannot determine the real images of the objects 102, 103 and the virtual images of the objects 102, 103, such that the processing circuit 112 cannot compute the position of object 102 and the position of object 103 correctly. The optical sensing system 100 of the prior art cannot be utilized to sense multiple objects for obtaining positions of the objects correctly.